The present invention relates generally to semiconductor processing techniques. More particularly, the invention includes a method and structure for forming an integrated spatial light modulator. Merely by way of example, the invention has been applied to a method of forming standoff structures in a bonded substrate structure and micro-electromechanical systems with reduced parasitic forces. The method and structure can be applied to other applications as well, such as actuators, sensors, detectors, and display components.
Spatial light modulators (SLMs) have numerous applications in the areas of optical information processing, projection displays, video and graphics monitors, and televisions. Reflective SLMs are devices that modulate incident light in a spatial pattern to reflect an image corresponding to an electrical or optical input. The incident light may be modulated in phase, intensity, polarization, or deflection direction. A reflective SLM is typically comprised of a one or two-dimensional array of addressable picture elements (pixels) capable of reflecting incident light. Source pixel data is first processes by an associated control circuit, then loaded into the pixel array, one frame at a time.
The fabrication processes used to manufacture SLMs are varied. In some of the fabrication processes, multiple substrates are bonded together to form the SLM structure. Some of these fabrication processes require alignment of the substrates prior to bonding, with tolerances on the order of microns, which may be a time consuming and expensive process.
In some SLM structures, micro-electromechanical systems (MEMS) are used to form micro-mirror arrays, sensors, and actuators. In some of these applications, a suspended member is attracted to an electrode upon application of an electrical force and restored to an original position by a restoring force. As the suspended member approaches the electrode, surface forces can exert influences on the MEMS. These surface forces are sometimes referred to as “stiction” forces, since in some MEMS, parasitic forces arise from a combination of MEMS components sticking together and from friction, thus the term stiction. These parasitic forces may be strong enough to overcome the restoring force, resulting in an undesirable adhesion of the suspended member to the electrode.
As merely an example, conventional MEMS have relied upon a variety of techniques to overcome such stiction forces. For example, certain devices have relied upon the coating of MEMS components and the use of complex mechanical structures. Unfortunately, these techniques also have limitations. For example, some coatings are difficult to deposit on small components and can require complex deposition equipment. Moreover, complex mechanical structures may have reliability and lifetime concerns.
Therefore there is a need in the art for improved methods and structures for fabrication processes for integrated SLMs and for methods and apparatus to reduce parasitic forces in electro-mechanical systems.